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https://github.com/cyyever/mariadb_modern_cpp


https://github.com/cyyever/mariadb_modern_cpp

cpp17 mariadb mysql

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mariadb modern cpp wrapper

====



This library is a lightweight modern wrapper around mariadb/mysql C api inspired by [sqlite_modern_cpp](https://github.com/SqliteModernCpp/sqlite_modern_cpp) and uses C++17.



```c++

#include 

#include 

using namespace mariadb;

using namespace std;



int main() {



   try {

      // connects to server

      mariadb::mariadb_config config;

      config.host = "xxx";

      config.port = 3306;

      config.user = "xxx";

      config.passwd = "xxx";

      config.default_database = "my_db";

      database db(config);



      // executes the query and creates a 'user' table

      db <<

         "create table if not exists user ("

         "   _id int primary key autoincrement not null,"

         "   age int,"

         "   name text,"

         "   weight real"

         ");";



      // inserts a new user record.

      // binds the fields to '?' .

      // note that only types allowed for bindings are :

      //      integer types(int, long, long long, etc)

      //      float types(float , double , etc)

      //      string (for CHAR,VARCHAR,TEXT columns)

      //      std::vector (for BLOB columns)

      //      std::optional (for NULL columns)

      db << "insert into user (age,name,weight) values (?,?,?);"

         << 20

         << "bob"

         << 83.25;



      int age = 21;

      float weight = 68.5;

      string name = "jack";

      db << "insert into user (age,name,weight) values (?,?,?);"

         << age

         << name

         << weight;



      //  gets the value generated for an AUTO_INCREMENT column by the previous INSERT or UPDATE statement.

      cout << "The new record got assigned id " << db.insert_id() << endl;



      // selects from user table on a condition ( age > 18 ) and executes

      // the lambda for each row returned .

      db << "select age,name,weight from user where age > ? ;"

         << 18

         >> [&](int age, string name, double weight) {

            cout << age << ' ' << name << ' ' << weight << endl;

         };



      // selects the count(*) from user table

      // note that you can extract a single culumn single row result only to : int,long,long,float,double,string,u16string

      int count = 0;

      db << "select count(*) from user" >> count;

      cout << "cout : " << count << endl;



      // you can also extract multiple column rows

      db << "select age, name from user where _id=1;" >> tie(age, name);

      cout << "Age = " << age << ", name = " << name << endl;



      // this also works and the returned value will be automatically converted to string

      string str_count;

      db << "select count(*) from user" >> str_count;

      cout << "scount : " << str_count << endl;

   }

   catch (exception& e) {

      cout << e.what() << endl;

   }

}

```



NOTES

----

Currently multi-statement execution is not supported.



Prepared Statements

----

It is possible to retain and reuse statments this will keep the query plan and in case of an complex query or many uses might increase the performance significantly.



```c++

database db(config);



// if you use << on a mariadb::database you get a prepared statment back

// this will not be executed till it gets destroyed or you execute it explicitly

auto ps = db << "select a,b from table where something = ? and anotherthing = ?"; // get a prepared parsed and ready statment



// first if needed bind values to it

ps << 5;

int tmp = 8;

ps << tmp;



// now you can execute it with `operator>>` or `execute()`.

// If the statement was executed once it will not be executed again when it goes out of scope.

// But beware that it will execute on destruction if it wasn't executed!

ps >> [&](int a,int b){ ... };



// after a successfull execution the statment can be executed again, but the bound values are resetted.

// If you don't need the returned values you can execute it like this

ps.execute();



// To disable the execution of a statment when it goes out of scope and wasn't used

ps.used(true); // or false if you want it to execute even if it was used



// Usage Example:



auto ps = db << "insert into complex_table_with_lots_of_indices values (?,?,?)";

int i = 0;

while( i < 100000 ){

   ps << long_list[i++] << long_list[i++] << long_list[i++];

   ps.execute();

}

```



Shared Connections

----

If you need the handle to the database connection to execute mariadb commands directly you can get a managed shared_ptr to it, so it will not close as long as you have a referenc to it.



Take this example on how to deal with a database backup using mariadbs own functions in a save and modern way.

```c++

try {

   database db(config);



   auto mysql_handle = db.connection();   // get a handle to the DB we want to backup in our scope

                                 // this way we are sure the DB is open and ok while we backup



   mysql_ping(mysql_handle.get());

} // Release allocated resources.

```



Transactions

----

All sql statements executed in a transaction context are commited as a transaction when the context is destructed,but if an exception is thrown,the transaction is canceled.



```c++

{

  auto ctx = db.get_transaction_context();

  db << "insert into user (age,name,weight) values (?,?,?);"

     << 20

     << "bob"

     << 83.25f;

  db << "insert into user (age,name,weight) values (?,?,?);"

     << 19

     << "chirs"

     << 82.7;

}



{

  auto ctx = db.get_transaction_context();

  db << "insert into user (age,name,weight) values (?,?,?);"

     << 20

     << "bob"

     << 83.25f;

  db << "insert into user (age,name,weight) values (?,?,?);"

     << 19

     << "chirs"

     << 82.7;

  throw std::runtime_error("Transaction will be canceled");

}



```



Blob

----

Use `std::vector` to store and retrieve blob data.  



You can also Use `std::vector` to store and retrieve blob data where `T` is a integer type,we will treat the vector as an continuous memeory block like `std::vector`.



```c++

db << "CREATE TABLE person (name TEXT, numbers BLOB);";

db << "INSERT INTO person VALUES (?, ?)" << "bob" << vector { 1, 2, 3, 4};



vector numbers_bob;

db << "SELECT numbers from person where name = ?;" << "bob" >> numbers_bob;



db << "SELECT numbers from person where name = ?;" << "sara" >> [](vector numbers_sara){

    for(auto e : numbers_sara) cout << (int)e << ' '; cout << endl;

};

```



NULL values

----

If you have databases where some rows may be null, you can use `std::unique_ptr` to retain the NULL values between C++ variables and the database.



```c++

db << "CREATE TABLE tbl (id integer,age integer, name string, img blob);";

db << "INSERT INTO tbl VALUES (?, ?, ?, ?);" << 1 << 24 << "bob" << vector { 1, 2 , 3};

unique_ptr ptr_null; // you can even bind empty unique_ptr

db << "INSERT INTO tbl VALUES (?, ?, ?, ?);" << 2 << nullptr << ptr_null << nullptr;



db << "select age,name,img from tbl where id = 1"

		>> [](unique_ptr age_p, unique_ptr name_p, unique_ptr> img_p) {

			if(age_p == nullptr || name_p == nullptr || img_p == nullptr) {

				cerr << "ERROR: values should not be null" << std::endl;

			}



			cout << "age:" << *age_p << " name:" << *name_p << " img:";

			for(auto i : *img_p) cout << i << ","; cout << endl;

		};



db << "select age,name,img from tbl where id = 2"

		>> [](unique_ptr age_p, unique_ptr name_p, unique_ptr> img_p) {

			if(age_p != nullptr || name_p != nullptr || img_p != nullptr) {

				cerr << "ERROR: values should be nullptr" << std::endl;

				exit(EXIT_FAILURE);

			}



			cout << "OK all three values are nullptr" << endl;

		};

```



You can use `std::optional` as an alternative for `std::unique_ptr` to work with NULL values.



```c++

#include 



struct User {

   long long _id;

   std::optional age;

   std::optional name;

   std::optional weight;

};



int main() {

   User user;

   user.name = "bob";



   // Same database as above

   database db(config);



   // Here, age and weight will be inserted as NULL in the database.

   db << "insert into user (age,name,weight) values (?,?,?);"

      << user.age

      << user.name

      << user.weight;

   user._id = db.last_insert_rowid();



   // Here, the User instance will retain the NULL value(s) from the database.

   db << "select _id,age,name,weight from user where age > ? ;"

      << 18

      >> [&](long long id,

         std::optional age,

         std::optional name

         std::optional weight) {



      cout << "id=" << _id

         << " age = " << (age ? to_string(*age) ? string("NULL"))

         << " name = " << (name ? *name : string("NULL"))

         << " weight = " << (weight ? to_string(*weight) : string(NULL))

         << endl;

   };

}

```



Errors

----



On error, the library throws an error class indicating the type of error. The error classes are derived from the mariadb::mariadb_exception class.

you can use `get_sql()` to see the SQL statement leading to the error.



```c++

database db(":memory:");

db << "create table person (id integer primary key not null, name text);";



try {

   db << "insert into person (id, name) values (?,?)" << 1 << "jack";

   // inserting again to produce error

   db << "insert into person (id, name) values (?,?)" << 1 << "jack";

}

/* if you are trying to catch all mariadb related exceptions

 * make sure to catch them by reference */

catch (mariadb_exception& e) {

   cerr  << e.what() << " during "

         << e.get_sql() << endl;

}

```



Building and Installing

----



The usual way works for installing:



```bash

mkdir build && cmake .. && make && sudo make install

```